Pseudomonas aeruginosa (P. aeruginosa) is a common opportunistic pathogen associated with bacterial keratitis, especially in extended wear contact lens users. Triggering receptors expressed on myeloid cells (TREMs) are a novel family of receptors that have been implicated as key molecules in development of the innate and adaptive immune responses, yet nothing is known about the role of TREMs in the cornea (or in the eye). Thus, we hypothesize that TREM-1 and -2 play critical roles in corneal inflammation to P. aeruginosa infection and regulate the disparate immune response to bacterial infection in the cornea of B6 (susceptible) vs. BALB/c (resistant) mice. Studies aimed at understanding the molecular mechanisms, particularly the early events of intracellular signaling and immunopathological processes involved in ocular immune response after P. aeruginosa infection, may provide a solution not only for control of bacterial keratitis, but for other diseases associated with excessive inflammation. The goal of this proposal is to elucidate the role of TREM-1 and -2 in the innate and adaptive immune response to P. aeruginosa infection resulting in corneal perforation (B6) vs. healing (BALB/c). Two specific aims are proposed and include: (1). TREM-1 dictates the susceptible outcome to P. aeruginosa keratitis by amplifying corneal inflammation. (2). TREM-2 promotes resistance against bacterial keratitis by attenuating corneal inflammation. Studies proposed herein will use multiple approaches to test the expression of TREM-1 and -2, their signaling pathways, and their immunoregulatory properties in P. aeruginosa keratitis. Experiments will include techniques such as ocular infection, bacterial plate counts, siRNA interference, LPS stimulation, cross-linking activation, histopathology, TransAM assay, myeloperoxidase (MPO) assay for PMN quantitation, peritoneal macrophage isolation, transient transfection, gene overexpression, western-blot, dual immunostaining, real-time PCR and enzyme linked immunosorbant assay (ELISA). Our long-term objective is to understand the pathophysiological mechanisms of disease in the P. aeruginosa infected mouse cornea in order to rationally develop therapies against keratitis for human patients. It is expected that our findings will be significant to the clinical care of patients with P. aeruginosa keratitis by providing potential targets for early therapeutic intervention. PUBLIC HEALTH RELEVANCE: Pseudomonas aeruginosa (P. aeruginosa) is a common opportunistic bacterial pathogen associated with sight-threatening corneal infections, especially in immuno-compromised patients and in extended wear contact lens users. In the United States the incidence of microbial keratitis due to contact lens use is 25,000-30,000 cases annually with the cost of treatment estimated at $15-30 million. Thus, the studies proposed in this application have relevance to human health as well as considerable medical and economic impact. It is expected that our findings will be significant to the clinical care of patients with P. aeruginosa keratitis by providing potential targets for early therapeutic intervention.